Conventionally, engine coolants for a vehicle engine cooling system contain an appropriate corrosion inhibitor to combat any impurities in the water which can cause corrosion in the radiator or heat exchanger, coolang passages of the engine block, the pump, the thermostat and the connecting pipes. The corrosion inhibitor typically restricts corrosion and may coat the exposed surfaces with a passive layer to protect the surface from corrosive water. However, different inhibitors are required for different circumstances depending on the materials employed, such as copper-brass or aluminum radiators.
The useful life of the corrosion inhibitor supplied in an ethylene glycol antifreeze is limited and the protective quality of the inhibitor will decrease with age. Obviously, the protection will decrease more rapidly if the coolant is lost through leakage, boil over, etc. To prevent corrosion, it has been proposed to place in the coolant system a quantity of a low solubility inhibitor product for continuous dissolution, however, the inhibitor product may be consumed before it is required and thus lose its effectiveness. The present invention overcomes these problems by providing a corrosion inhibitor that is withheld from contact with the coolant until the corrosive characteristics of the liquid are such as to require additional inhibitor to prevent corrosion in the coolant system and in the heat exchanger in particular.